The fixation and/or stabilization of bones and/or bone fragments is/are commonly required by orthopedic surgeons to treat injuries such as fractures or disease. To accomplish this, the bones/bone fragments can be joined by a rod, plate or the like, which is fixed to the bones/bone fragments via fasteners such as screws, pins or the like. The connection by the rod(s), plate(s) or the like maintains the bones/bone fragments in a desired orientation and/or at desired spacings, positions, etc. Different situations often require the adjustment of such spacings or orientations, or the removal of the apparatus, sometimes with replacement by another apparatus. For these reasons it is useful to provide fasteners that can be fixed or released, and can also articulate to adjust relative to the rod, plate, or the like, as required by the arrangement of the bones/bone fragments being treated.
In spinal surgery, it is often necessary to secure various implants to the vertebrae and interconnect the vertebrae by attaching one or more rods or plates to the implants. Due to the complex curvature of the spine, as well as irregularities of the same that often need to be treated, it is often difficult to align a rod or plate with all of the implants/fasteners fixed to the various vertebrae to be connected via the rod or plate. By providing fasteners that have some articulation ability, this allows more flexibility in joining the fasteners (and thus the vertebrae that they are attached to) to a rod or plate in the orientations needed.
In some surgeries, it is necessary to span multiple vertebrae of the spine with rods that provide stabilizing forces to the vertebrae to help maintain the desired orientations of the vertebrae o maintain a desired curvature in the spine. In these instances, uniplanar fasteners that allow pivoting in only one plane can be useful, as opposed to the more commonly used polyaxial screws, as polyaxial screws may be more likely to fail by rotating rather than withstanding a lateral force applied to the rod therethrough.
In any case, once the polyaxial or uniplanar fastener has been articulated to the desired angular position of the screw shaft relative to the tulip, there needs to be a mechanism for maintaining that angular position/orientation in a fixed manner, as the orientation should be maintained upon completing the procedure. There is a continuing need for improved fixation mechanisms to maintain fasteners in their desired orientation during use after completion of the procedure.